The present invention relates to a cylinder head cover fixed to a cylinder head of an internal combustion engine. The present invention further relates to a method for mounting a cylinder head cover to a cylinder head.
Conventionally, internal combustion engines are known in which an oil control valve for controlling supply and drainage of hydraulic oil to and from a variable valve actuation mechanism is attached to a cylinder head cover (for example, refer to Japanese Patent No. 3525709).
Typically, such a cylinder cover is formed to have relatively thin walls to reduce the weight. This reduces the rigidity of the cylinder head cover compared to that of the cylinder head. Therefore, when such a cylinder head cover is fixed to a cylinder head, the cover could be deformed. Such deformation can deform a portion of the cover to which an oil control valve is attached. As a result, supply and drainage control performed by the valve is likely to be adversely affected.
Accordingly, in the configuration disclosed in the document, the cylinder head cover includes a main body fixed to a cylinder head and a valve case that is formed separately from the main body and receives an oil control valve. In this configuration, deformation of the cover is hardly transmitted to the portion of the valve case to which the valve is attached. Thus, the attaching portion is hardly deformed.
In the configuration disclosed in the above patent, a flange is formed on a surface (contacting surface) of the valve case that contacts the cylinder head cover. The valve case is placed on the cylinder head cover main body with the flange contacting an upper surface (outer surface) of the cylinder head cover main body. The valve case is then fixed to the cylinder head cover main body with bolts. Further, in the above-described configuration, a variable valve actuation mechanism is provided in the cylinder head. An oil passage for supplying and draining hydraulic oil to and from the variable valve actuation mechanism extends through both of the cylinder head and the oil control valve. The passage thus has a separated structure, that is, the passage has a section formed in the valve case and a section formed in the cylinder head. In other words, the oil passage having separate sections has a joint.
When securing the cylinder head cover main body to attach the valve case to the cylinder head, an upper surface of the cylinder head in which an opening of the oil passage is formed is pressed downward by a lower surface of the valve case. This guarantees the sealing performance at the joint in the oil passage and facilitates the assembly.
However, when the valve case is attached so that the pressing occurs, the reaction force applied to the valve case from the cylinder head acts as external force (separating force) that pushes the valve case away from the upper surface of the cylinder head cover. The separating force acts to degrade the attachment of the valve case to the cylinder head cover. Further, such separating force is likely to a produce local reaction force in the valve case and the cylinder head cover main body, which can deform the valve case and the cylinder head cover main body. As a result, the portion of the valve case to which the oil control valve is attached is likely to be deformed.
Since the rigidity of the cylinder head cover main body is likely to be reduced as described above, vibrations transmitted from the engine to the cylinder head cover main body can further degrade the state of attachment.